The (Al,Ga,In)N material system includes materials having the general formula AlxGayIn1−x−yN where 0≦x≦1 and 0≦y≦1. In this application, a member of the (Al,Ga,In)N material system that has non-zero mole fractions of aluminum, gallium and indium will be referred to as AlGaInN, a member that has a zero aluminum mole fraction but that has non-zero mole fractions of gallium and indium will be referred to as InGaN, a member that has a zero indium mole fraction but that has non-zero mole fractions of gallium and aluminum will be referred to as AlGaN, and so on. There is currently considerable interest in fabricating semiconductor light-emitting devices in the (Al,Ga,In)N material system since devices fabricated in this system can emit light in the blue wavelength range of the spectrum. Semiconductor light-emitting devices fabricated in the (Al,Ga,In)N material system are described in, for example, U.S. Pat. No. 5,777,350.
FIG. 1 is a schematic view of a semiconductor laser device or laser diode (ID) fabricated in the (Al,Ga,In)N material system. The device is able to emit light in the blue wavelength range, in the 380 nm to 450 nm wavelength range.
The laser diode 18 of FIG. 1 is grown over a substrate 1. In the laser diode 18 of FIG. 1 the substrate 1 is a template substrate consisting of an n-type doped GaN layer 3 grown over a sapphire base substrate 2. A buffer layer 4, a first cladding layer 5 and a first optical guiding layer are grown, in this order, over the substrate 1. In the embodiment of FIG. 1 the buffer layer 4 is a n-type GaN layer, the first cladding layer 5 is an n-type AlGaN layer, and the first optical guiding layer is an n-type GaN layer.
An active region 7 is grown over the first optical guiding layer 6.
A second optical guiding layer 8, a second cladding layer 9 and a cap layer 10 are grown, in this order, over the active region 7. The second optical guiding layer 8 and second cladding layer 9 have opposite conductivity type to the first optical guiding layer 6 and first cladding layer 5. In the laser diode 18 of FIG. 1 the second optical guiding layer 8 is a p-type GaN layer, the second cladding layer 9 is a p-type AlGaN layer, and the cap layer 10 is a p-type GaN layer.
The active region 7 of the laser device 18 shown in FIG. 1 is a multiple quantum well (MQW) active region, and contains a plurality of quantum well layers 12,14,16. Each quantum well layer 12,14,16 is sandwiched between two barrier layers 11,13,15,17. In the laser device 18 of FIG. 1, the lowermost barrier layer 11 and the uppermost barrier layer 17 are AlGaN layers. The intermediate barrier layers 13,15 may be, for example, layers of InxGa1−xN (0≦x≦0.05), AlxGa1−xN (0≦x≦0.4) or AlGaInN. The quantum well layers 12,14,16 may be, for example, layers of InxGa1−xN (0≦x≦0.3), AlxGa1−xN (0≦x≦0.1) or AlGaInN.
FIG. 1 shows a laser device having an MQW active region. A laser fabricated in the (Al,Ga,In)N system may alternatively have a single quantum well (SQW) active region that contains a single quantum well layer. In such a laser, the upper AlGaN barrier layer 17 would be grown directly on the first quantum well layer 12. The second and third quantum well layers 14,16 and the intermediate barrier layers 13,15 would be omitted.
Where the laser device 18 has a MQW active region, the active region is not limited to three quantum well layers as shown in FIG. 1. An MQW active region may have two quantum well layers or it may have three or more quantum well layers.
The structure of the laser 18 of FIG. 1 is described in more detail in co-pending UK patent application No. 0325100.6, having the same filing date as the present application.